I already answered this on the DBI mailing list, but just so its here also... DBD::Pg is only checking for the correct number of arguments to execute() IF you supply arguments.

Sounds like a bug to me, and shouldn't be too hard of a patch for someone to write. DBD::Oracle has similar XS code, but since Oracle natively supports placeholders, you end up with an Oracle error if you don't supply any args to a statement with placeholders. The DBD::Pg XS code needs to do the checking explicitly itself.